This invention relates to a color field sequential projection system including a polarized light beam splitter and an electronically controllable birefringence quarter waveplate and, more particularly, to an electronically controllable birefringence quarter waveplate which allows for improved contrast performance and color purity in a color field sequential projector using a polarized light beam splitter.
Conventional projection systems comprise a reflective liquid crystal display (LCD) device and a polarized light beam splitter (PBS) prism to produce a projected image. A quarter waveplate may be introduced between the PBS prism and the LCD panel to compensate for depolarization in the skew rays of light passing through the prism. This compensation is believed to be necessary to achieve the best dark state of the projected image and, therefore, the best contrast ratio. The quarter waveplate is usually optimized for the waveband illuminating the LCD panel. Accordingly, in a three panel system a red optimized quarter waveplate is placed in front of the red LCD device, a green optimized quarter waveplate is placed in front of the green LCD device, and a blue optimized quarter waveplate is placed in front of the blue LCD device. In other words, the three different quarter waveplates are each optimized for a particular and unique waveband.
In a color field sequential projector using a single LCD panel, however, the single panel is exposed to multiple wavebands of light as the display sequences through the display of the red, green and blue images that make up the full color projection. For optimum dark level, an optimized quarter waveplate would have to be physically switched in front of the LCD as the illumination waveband changes. Due to applicable time constraints, this application has not been pursued. Accordingly, prior art projection systems utilizing only a single LCD panel do not use a quarter waveplate positioned between the PBS prism and the LCD panel. There appears to be no prior art solution to improve contrast performance and color purity in a color field sequential projector using a polarized light beam splitter.
The assembly of the present invention provides an electronically controllable quarter waveplate positioned between an LCD panel and the polarized light beam splitter, wherein the controllable quarter waveplate can be switched to be optimum for each waveband as the illumination distribution changes in the color field sequence. In other embodiments, multiple controllable quarter waveplates may be used in a single projector system.
Accordingly, an object of the invention is to provide a color field sequential projector including an electronically controllable quarter waveplate.
Another object of the invention is to provide a color field sequential projector including an electronically controllable quarter waveplate, a PBS prism and at least one LCD panel.
A further object of the invention is to provide a color field sequential projector including a quarter waveplate that can be switched to be optimum for each waveband as the illumination distribution changes in the color field sequence.